London, Jun 30: Roger Federer and Andy Murray are locked on collision course for a dream Wimbledon final, but a giant Croatian and a wily Spaniard stand in their quarter-final paths on Wednesday.
Federer will be playing his 25th Grand Slam quarter-final while 6ft 10in (2.08m) Ivo Karlovic has never before got this far in the majors.
But he still represents a huge barrier to Federer's ambitions of winning a record 15th Grand Slam title having not faced a break point in four rounds so far.
Federer holds an 8-1 career record over Karlovic and insists he will relish facing the 22nd seed who has now fired down 137 aces in his four matches.
"I like these sort of challenges," said five-time champion Federer.
"But I like to beat this guy because he makes it hard on us to beat him. He's become an excellent player. He's not to be underestimated."
Murray, bidding to become Britain's first male champion since Fred Perry in 1936, needed five sets to get past Switzerland's Stanislas Wawrinka in the fourth round on Monday.
It was the latest ever finish to a Wimbledon match courtesy of the Centre Court's 80million-pound roof being rolled out for the first time.
Murray now faces Spain's former world number one, and French Open winner, Juan Carlos Ferrero for a place in the last four.
"Ferrero is a very tough player on virtually all surfaces," said the Scotsman who won the pair's only previous meeting on grass in the semi-finals at Queen's this month.
"I played great at Queen's but if I play poorly on Wednesday there's a good chance I will lose."
Ferrero, now ranked at 70 in the world, was a quarter-finalist here in 2007 and is the first wildcard to reach the last eight since Goran Ivanisevic in 2001. That year, Ivanisevic famously won the title.
"I have a little bit more rhythm than that week (at Queen's). I have learned some things. I have to do my job, be aggressive all the time, because he likes to play at one level, and then change the rhythm very fast," said Ferrero.
If Murray gets to the semi-finals, then either 2002 champion Lleyton Hewitt or two-time runner-up Andy Roddick will be waiting for him.
Hewitt, the only Australian in the draw, insists he has nothing to fear from the sixth seed after staging his fifth career comeback from two sets to love down to beat Czech 23rd seed Radek Stepanek 4-6, 2-6, 6-1, 6-2, 6-2.
That victory, and his second round triumph over fifth seed Juan Martin Del Potro, have given the 28-year-old a huge boost following last year's hip surgery.
Hewitt felt he had the better of Roddick at Queen's earlier this month when he lost in the third round in two tiebreaks.
"Queen's was only one or two points. I felt like I had the better of him in the actual service games that we were playing," Hewitt said.
Hewitt has won six of the pair's 11 meetings, but the American has won the last four, a run stretching back over four years.
"It doesn't get any easier from here. I have loads of respect for Lleyton and what he's been able to accomplish," said Roddick who made the quarter-finals with a straight sets win over Czech Tomas Berdych.
In the remaining quarter-final, Germany's Tommy Haas, the oldest man in the draw at 31, faces Serbian fourth seed Novak Djokovic.
It will be Haas's first Wimbledon quarter-final having first competed here in 1997.
The German is nine years older than Djokovic, but has the advantage of having beaten the world number four in the final at Halle on grass on the eve of Wimbledon.
Haas, who saved two match points in his marathon third round win over Marin Cilic, insists his age won't be a factor.
"Age is just a number," said Haas, who made the last eight with a convincing 7-6 (10/8), 6-4, 6-4 win over Russia's Igor Andreev.
Djokovic, a semi-finalist in 2007, has made the quarter-finals almost unnoticed as focus has fallen on Federer and Murray.
"Tommy is a great player, and he's playing really well lately," said the Serbian who cruised past Israel's Dudi Sela in the last 16.